This invention is related to a process known as the "Solvay Process" for the synthetic production of sodium carbonate from sodium chloride solutions, and it is intended mainly to obtain sodium carbonate secondarily from the waste known as FLP liquor of the process, thereby to negate the production of refuse and to increase the obtention of secondary products such as ammonium chloride and calcium chloride. In a conventional Solvay process for the primary obtention of sodium carbonate, the sodium chloride found in ore deposits is dissolved, so as to be pumped towards the treating plant where, after being purified in order to eliminate its impurities (generally consisting of Ca.sup.++ and Mg.sup.++), it is fed into an absorption tower where it will contact gaseous ammonia and carbon dioxide, thus producing an ammoniated and carbonated brine called CB liquor, according to the following reactions: EQU NH.sub.3 +H.sub.2 O.fwdarw.NH.sub.4 OH+Q.sub.1 ( 1) EQU CO.sub.2 +H.sub.2 O.fwdarw.H.sub.2 CO.sub.3 +Q.sub.2 (2)
First of all, the CB liquor is generally passed through a carbonation column which is in the stage of washing and disincrustation or descaling of sodium bicarbonate so as to precarbonate it, whereby a precarbonated liquor known as CLP liquor is produced. This CLP liquor is then circulated through the carbonation columns in which it will counter-currently contact the gases derived from several concentrations of carbon dioxide (Top gas introduced at an adequate height into the middle part of the column and which contains nitrogen and approximately 42% of CO.sub.2, and Bottom gas introduced through the bottom of the column and which contains nitrogen and approximately 75% of CO.sub.2), thus producing a liquor known as CL liquor containing sodium bicarbonate in suspension, according to the following reactions: EQU NH.sub.4 OH+H.sub.2 CO.sub.3 .fwdarw.NH.sub.4 HCO.sub.3 +H.sub.2 O+Q.sub.3 ( 3) EQU NH.sub.4 HCO.sub.3 +NaCl.revreaction.NaHCO.sub.3 +NH.sub.4 Cl+Q.sub.4 ( 4)
The Cl liquor containing the sodium bicarbonate in the form of a precipitate, ammonium chloride in which the ammonia is fixed as well as small quantities of reagents which did not react (NaCl, NH.sub.4 HCO.sub.3, H.sub.2 O), is then filtered to obtain sodium bicarbonate in the form of a cake which dries and calcinates afterwards, so as to obtain sodium carbonate or light soda ash as a product and to recover part of the CO.sub.2, NH.sub.3 and H.sub.2 O in gaseous form, according to the following reactions: EQU 2NaHCO.sub.3 +.DELTA..fwdarw.Na.sub.2 CO.sub.3 +CO.sub.2 +H.sub.2 O (5) EQU NH.sub.4 HCO.sub.3 +.DELTA..fwdarw.NH.sub.3 +CO.sub.2 +H.sub.2 O (6)
on the first hand; and on the other hand a residual filtrate called FLP liquor composed chiefly of sodium chloride, ammonium bicarbonate, ammonium chloride and carbon dioxide.
In the conventional processes known at present the FLP waste liquor is subjected directly to distillation in order to recuperate a good part of free ammonia and CO.sub.2, causing it to react with milk of lime in the section called PLM, in order to transform the ammonium chloride into ammonium hydroxide and calcium chloride into a final liquor known as DS integral, according to the following reactions: EQU 2NH.sub.4 Cl+Ca(OH).sub.2 .fwdarw.2NH.sub.4 OH+CaCl.sub.2 (7)
This DS integral liquor, which in fact keeps the same great volume of FLP liquor, is passed on to a solid separating plant at which DS sludge and a clear DS liquor are obtained. If calcium chloride is marketable, the same is extracted and the residual sludge is wasted along with the residual clear DS liquors. Obviously then, almost all of the plants for the industrial obtention of sodium carbonate which use the aforementioned Solvay process have to face the enormous problem of the production of a great volume of refuse, starting from the stage of separation of the sodium bicarbonate cake and the FLP liquor. Besides, in case it were possible to increase the production of the existing industrial plants, which as yet is not possible at these, because the production is based upon the reaction of ammonium bicarbonate with sodium chloride in the original carbonation reaction in accordance with equation No. 4, the maximum production of which is determined by the balance in the reaction, said circumstance will also cause cause a proportional increase of refuse liquor (whether of FLP liquor or of clear DS liquor). Additionally, even though some useful products could be derived from the waste liquors, there would still be a great volume of refuse. On the other hand, some research projects have been carried out in order to reduce the concentrations of noxious salts in the waste liquors, thus trying to recuperate a few secondary products such as ammonium chloride, for its use such as in the case of a dual process put into practice in Japan.
In this process ammonia is aggregated to FLP liquor and this is then cooled to precipitate the ammonium chloride, afterward adding sodium chloride to the remaining liquor so as to recirculate it to the precarbonator and to the carbonation tower, in order to re-use the ammonia and the carbon dioxide found in the same with a minimum of DS waste liquors. Nevertheless, and contrary to the possibility of increasing the production of sodium carbonate by recirculating the saturated liquor through the aggregation of salts (after the stage of cooling and of precipitation of the ammonium chloride), in the stage of carbonation the production of sodium carbonate keeps constant due to the reversible nature of the reaction which develops in the carbonator, which generally has a yield of 75% (equation No. 4). However, the possibility of obtaining a secondary production of sodium carbonate from other sources within the same process, has been neither envisioned nor studied thus far and there has been only one primary source for the production of sodium carbonate. To be inferred from the above, intense researching has been done in order to take advantage of the waste liquors, to recuperate part of the raw-materials normally consisting of carbon dioxide and ammonia and re-use them in the process.
In order to increase the production of sodium carbonate in the carbonation columns and to improve the size of the product's grain, several research projects were implemented to study the behavior of the operating conditions present in the carbonation columns. It was found that the carbonation columns were exceeded as to the per-column production capacity which caused a high flux both of carbon dioxide and ammonia gases, and of feeding liquor above their design values, thus affecting the time of residence and not allowing the reaction to take place in a satisfactory manner for want of area and time of contact, as observed in the analyses of the column discharges which contained a high degree of CO.sub.2, indicating a poor absorption of CO.sub.2. On this account the particles of sodium bicarbonate formed in the reaction were affected in their growth. It was precisely during said study that, through a series of laboratory analyses effecting the column discharge of the filtered liquor, it was observed that there existed stoichiometrical quantities of raw materials required for a greater precipitation of crystals of sodium bicarbonate. However, said precipitation had never been carried out, due mainly to the already known reason that, as the principal reaction between the sodium bicarbonate and the ammonium chloride reached its point of equilibrium it resulted in that, within the time determined by the reversible nature of this reaction the same moles produced on the right side of the reaction were the same as those on the left and so on; with no precipitation taking place at this point. Considering that, as it is well known, the constant of equilibrium is a function of the products of the concentrations of the products and of the reagents, the increase or decrease of any of them will alter the balance of the reaction in one way or another.
The foregoing situation led this inventor to take into account that, in order to precipitate a secondary quantity of sodium bicarbonate it was necessary to increase the concentration of one of the reagents in the FLP waste liquor, so as to cause the reaction to move to the right. Since the raw material more ready at hand was sodium chloride, it was decided to increase the concentration of same in the FLP liquors, which resulted in an amazing precipitation of a considerable quantity of crystals which were identified as crystals of sodium bicarbonate. It was also observed that this reaction could occur with other compounds or compound mixtures which included sodium (or alkaline metal) ions, such as sodium hydroxide or sodium sulfate, with which ammonium sulfate could be obtained as a secondary product, thus being useful in other industries. Notwithstanding the above, it is possible to increase the concentration of the other reagent, this is to say, the ammonium bicarbonate (as free ammonia) or gaseous ammonia and CO.sub.2 in the FLP liquor, in order to accomplish the secondary production of sodium carbonate. But this reaction does not have a yield as high as the one in which sodium chloride is used.